Methods, apparatus, equipment and storage media for assessing the transient stability of branch energy in grid-connected wind turbine systems.

Abstract

This application provides a method, apparatus, device, and storage medium for evaluating the transient stability of branch energy in a grid-connected wind turbine system. It relates to the field of wind power generation technology. The method includes: constructing a branch energy function for the grid-connected wind turbine system based on the mathematical characteristics of a phase-locked loop and the voltage distribution characteristics in the network; and determining the branch stability discrimination index (BSC) of the grid-connected wind turbine system based on the branch energy function. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If the value is not equal to 0, the system is transiently stable. This application constructs a four-unit, two-zone simulation model with grid-connected wind turbines on the DIgSILENT / PowerFactory platform to verify the effectiveness of the proposed system stability index.

Description

Technical Field

[0001] This application relates to the field of wind power generation technology, and in particular to a method, apparatus, equipment and storage medium for evaluating the transient stability of branch energy in a grid-connected wind turbine system. Background Technology

[0002] With the rapid increase in the proportion of renewable energy power generation, the transient stability problems caused by grid-connected wind turbines via power electronic converters are becoming increasingly prominent. Traditional power system transient stability analysis mainly relies on synchronous machine electromechanical transient models, using methods such as power angle trajectory and transient energy function to assess system stability. However, grid-connected wind turbines have characteristics such as lack of inertia, fast control response, and limited fault ride-through capability. The dynamic process of their grid-connected systems exhibits multi-timescale coupling characteristics, making it difficult for traditional energy assessment indicators based on synchronous machine-dominated modes to accurately characterize the transient stability boundary of the wind turbine grid-connected system. Existing research mainly focuses on converter-level control strategy optimization or system-level voltage / frequency stability analysis, leaving a theoretical gap in the quantitative assessment of transient stability at the branch energy level. In particular, under fault impact, the spatiotemporal distribution characteristics of grid branch energy in wind turbine grid-connected systems undergo significant distortion, and conventional energy flow calculation methods cannot effectively capture the modulation effect of converter dynamics on branch energy, leading to biases in the assessment of stability margins of key transmission sections. There is an urgent need to build a branch energy transient stability assessment system that adapts to the dynamic characteristics of power electronic equipment in order to solve the problem of system stability judgment under the environment of high proportion of new energy grid connection. Summary of the Invention

[0003] This application provides a method, apparatus, equipment, and storage medium for evaluating the transient stability of branch energy in a grid-connected wind turbine system. It aims to solve the problem of transient stability judgment in new scenarios for grid-connected wind turbine systems. Combining the mathematical characteristics of phase-locked loops and the voltage distribution characteristics in the network, a branch energy function for the grid-connected wind turbine system is constructed. Based on the distribution characteristics of branch energy under different system stability conditions, key system stability factors inherent in the branches are extracted, and a system stability index based on branch information is constructed. A four-machine, two-zone simulation model containing grid-connected wind turbines is built on the DIgSILENT / PowerFactory platform to verify the effectiveness of the proposed system stability index.

[0004] In a first aspect, this application provides a method for assessing the transient stability of branch energy in a grid-connected wind turbine system, including:

[0005] Based on the mathematical characteristics of phase-locked loops and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed.

[0006] Based on the branch energy function, determine the branch stability discrimination index (BSC) for the grid-connected wind turbine system. GFLWT If a branch BSC exists after a fault occursGFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If ≠0, the system is transiently stable.

[0007] In one possible design, based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed, including:

[0008] Based on the established assumptions, the equivalent motion equations of the grid-type wind turbine are established;

[0009] Based on the equivalent motion equation of the grid-type wind turbine, an energy function is constructed.

[0010] Based on the grid-connected infinite bus system of grid-connected wind turbines, the state-space expression of the grid-connected multi-machine system of grid-connected wind turbines is obtained by extending to multi-machine systems.

[0011] Based on the state-space expression of the grid-connected multi-machine system and the energy function, the branch energy function of the grid-connected multi-machine system is constructed. The branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

[0012] In one possible design, the established assumptions include:

[0013] Ignore the transient processes of the mechanical rotor and PWM in the grid-type direct-drive fan;

[0014] Assuming the DC voltage is stable, the dynamic characteristics of the rotor-side converter are ignored;

[0015] Ignoring current loop dynamics and using unity power factor control, there exists a q-axis reference current of 0;

[0016] Assuming the voltage loop control parameters are constant, the dynamics of the voltage control loop are not considered in the transient stability analysis of grid-connected wind turbines.

[0017] Based on the established assumptions, the equivalent motion equations for the grid-type wind turbine are established, including:

[0018] A mathematical model of a grid-connected wind turbine system is constructed based on the established assumptions; wherein, the phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows:

[0019] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0020] In the formula: U 1,q Let K be the q-axis component of the voltage at U1. pK is the proportional gain of the phase-locked loop. i ω is the integral coefficient of the phase-locked loop. N θ is the system's rated angular frequency. pll The phase angle is the output phase angle of the phase-locked loop, and t is time.

[0021] Based on the distribution law of the q-axis component of the voltage at each node on the branch and the phase-locked loop control structure, the equivalent motion equation of the grid-type wind turbine is established.

[0022] The distribution pattern of the q-axis components of the voltage at each node on the branch is as follows:

[0023]

[0024] In the formula: ω pll To generate a reference frame for the rotational speed of the grid-type wind turbine control system, L 12 L 13 L 14 θ1, θ2, θ3, and θ4 are the line inductances from node 1 to nodes 2, 3, and 4, respectively, and θ4 are the voltage phase angles at nodes 2, 3, and 4. The power factor angle is the angle under unity power factor control. θ 12 θ 13 θ 14 Let θ be the impedance angle of lines 1-2, 1-3, and 1-4. 12 =θ 12 =θ 14 =90°; the line current component on the q-axis is I g The value is constant, and δ is the difference between the phase angle of the phase-locked loop output and the phase angle of the voltage at the infinite point.

[0025] The equivalent motion equation of the grid-connected wind turbine is expressed as:

[0026]

[0027] In the formula: U1, U2, U3, and U4 are the voltages at nodes 2, 3, and 4, respectively.

[0028] In one possible design, based on the grid-connected infinite bus system of grid-connected wind turbines, the system is extended to a multi-machine system, resulting in the state-space expression of the grid-connected infinite bus system of grid-connected wind turbines as follows:

[0029]

[0030] In the formula: V is the total energy of the system, V KE For the system's kinetic energy, V PE For the system's transient state energy, V D For the system damping energy, σ k Let σ be the phase angle difference of line k.k,s Let P be the phase angle difference of line k under the steady state of the system, M be the equivalent inertial time constant, and P be the phase angle difference of line k. k (δ) represents the equivalent electromagnetic power, P k,s U is the equivalent power steady-state value, D is the damping coefficient of the grid-connected wind turbine, and U is the damping coefficient of the grid-connected wind turbine. j,q For U j The q-axis component of the voltage at the location, l 1j Let U be the line inductance from node 1 to node j. j Let be the voltage at node j, u be the branch phase angle difference, k be the line number, and t0 be the moment when the system is in steady state.

[0031] In one possible design, based on the state-space expression of the grid-connected multi-unit wind turbine system and the energy function, the branch energy function of the grid-connected wind turbine system is constructed, including:

[0032] Based on the state-space expression of the grid-connected multi-unit wind turbine system and the energy function, according to the equilibrium point (α) s ,0), establish the energy function for the entire system:

[0033]

[0034] In the formula: Let W(α,α) be the kinetic energy function. s Let ) be the potential energy function, where Let V(α,ω) be the damping energy function. g () represents the total energy of the system. M is the transpose of the generator angular velocity vector. g Let ω be the equivalent inertial time constant matrix. g Let α be the generator angular velocity vector. s Let f(α) be the steady-state phase angle of the node voltage relative to the reference point, α be the phase angle of the node voltage relative to the reference point, D be the generator damping coefficient matrix, and f(α) be the generator damping coefficient matrix. s ) represents the steady-state value of the equivalent active power of each branch, and f(α) represents the equivalent active power of each branch;

[0035] Using the branch phase angle difference at the fault clearing moment as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0036]

[0037] Where: V is the total system energy, i is the generator serial number, m is the total number of GFL-PMSG units, and M is the total number of units. i Let ω be the equivalent inertial time constant of the i-th generator. i Let D be the angular frequency of the i-th generator. i Let be the damping coefficient of the i-th generator.

[0038] In one possible design, the branch stability discrimination index (BSC) of the grid-connected wind turbine system is determined using the following formula. GFLWT :

[0039]

[0040] In the formula: V' PEK (t a ,t b ) = V PEK (t a ,t b ) / (1-K p l 1j I g To eliminate the form of internal parameters of the grid-type fan, K p l is the proportional gain of the phase-locked loop. 1j V is the line inductance from node 1 to node j. PEK (t a ,t b ) is branch k in (t) a ,t b The change in branch potential energy at time ) U j,q (t b ) for t b The voltage component of node j at time q, U j,q (t0) represents the voltage component of node j at time t0 along the q-axis.

[0041] In one possible design, the branch stability discrimination index is used to determine the changing trend of the branch angle difference, taking the initial power flow direction of branch k as the positive direction, in (t a ,t b It exists throughout the time period. When Δω k When (t) < 0, if BSC GFLWT <0, then [P k (t)-P k,s ] < 0,; ​​when Δω k When (t)>0, if BSC GFLWT >0, then [P k (t)-P k,s >0; where, The derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy in branch k, P k (t) represents the equivalent power of branch k at time t, P k,s This represents the equivalent power at the steady moment of branch k.

[0042] Secondly, this application provides a branch energy transient stability assessment device for a grid-connected wind turbine system, the device comprising:

[0043] The function construction module is configured to construct the branch energy function of the grid-connected wind turbine system based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network.

[0044] The indicator evaluation module is configured to determine the branch stability discrimination index (BSC) of the grid-connected wind turbine system based on the branch energy function. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If ≠0, the system is transiently stable.

[0045] Thirdly, embodiments of this application provide an electronic device, including: at least one processor and a memory; the memory stores computer execution instructions; the at least one processor executes the computer execution instructions stored in the memory, causing the at least one processor to execute the branch energy transient stability assessment method for a grid-connected wind turbine system as described in the first aspect and various possible designs of the first aspect.

[0046] Fourthly, embodiments of this application provide a computer-readable storage medium storing computer-executable instructions. When a processor executes the computer-executable instructions, it implements the branch energy transient stability assessment method for grid-connected wind turbine systems as described in the first aspect and various possible designs of the first aspect.

[0047] Fifthly, embodiments of this application provide a computer program product, including a computer program that, when executed by a processor, implements the branch energy transient stability assessment method for a grid-connected wind turbine system as described in the first aspect and various possible designs of the first aspect.

[0048] The method, apparatus, equipment, and storage medium for assessing the transient stability of branch energy in a grid-connected wind turbine system provided in this application have at least the following beneficial effects:

[0049] 1) This application constructs a branch energy model under the grid-connected wind turbine system, which completes the branch energy model system.

[0050] 2) The branch energy transient stability assessment index of the grid-connected wind turbine system proposed in this application can determine the weak link of the system through network variables, and thus determine the stability of the system. It has the advantages of being simple and easy to obtain.

[0051] 3) The numerical example analysis shows that the branch energy transient stability evaluation index of the grid-connected wind turbine system proposed in this application does not require the calculation of critical energy and can quantify the stability of the system. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0053] Figure 1 A flowchart of a method for evaluating the transient stability of branch energy in a grid-connected wind turbine system provided in this application embodiment;

[0054] Figure 2 The topology diagram of the GFLWT grid-connected infinite bus system provided in the embodiments of this application;

[0055] Figure 3 This is a flowchart illustrating the construction of the branch energy function of a grid-connected wind turbine system provided in an embodiment of this application.

[0056] Figure 4 The graphs are transient energy curves of each branch under stable and unstable conditions of the GFLWT grid-connected infinite bus system according to an embodiment of this application; wherein, (a) is the transient energy change curve of each branch under stable condition; and (b) is the transient energy change curve of each branch under unstable condition.

[0057] Figure 5 This is a diagram of a 4-machine, 2-zone system under GFLWT access according to an embodiment of this application:

[0058] Figure 6 The graphs are transient energy curves of each branch under stable and unstable conditions in the GFLWT access 4-machine 2-zone system of this application embodiment; wherein, (a) is the transient energy change curve of each branch under stable condition; and (b) is the transient energy change curve of each branch under unstable condition.

[0059] Figure 7 This is a structural diagram of the branch energy transient stability assessment device for a grid-connected wind turbine system provided in an embodiment of this application.

[0060] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0061] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0062] The collection, storage, use, processing, transmission, provision, and disclosure of financial data or user data involved in the technical solution of this application all comply with the provisions of relevant laws and regulations and do not violate public order and good morals.

[0063] It should be noted that in the embodiments of this application, certain software, components, models and other existing solutions in the industry may be mentioned. These should be regarded as exemplary and are only intended to illustrate the feasibility of implementing the technical solution of this application. However, it does not mean that the applicant has used or necessarily used the solution.

[0064] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0065] This application provides a method for evaluating the transient stability of branch energy in a grid-connected wind turbine system. For example... Figure 1 The diagram shows a flowchart of a branch energy transient stability assessment method for a grid-connected wind turbine system provided in this application embodiment. The branch energy transient stability assessment method for a grid-connected wind turbine system includes the following steps S100-S200.

[0066] S100: Based on the mathematical characteristics of phase-locked loops and the voltage distribution characteristics in the network, construct the branch energy function of the grid-connected wind turbine system.

[0067] In some embodiments, such as Figure 2 The diagram shown is a topology diagram of a GFLWT grid-connected infinite bus system provided in an embodiment of this application. Based on this GFLWT grid-connected infinite bus system, as... Figure 3 As shown, the branch energy function of the grid-connected wind turbine system is constructed through the following steps:

[0068] S101: Based on the set assumptions, establish the equivalent motion equations for the grid-type wind turbine.

[0069] In this embodiment, in order to accurately describe the transient characteristics of the phase-locked loop, based on the above analysis, the following assumptions are proposed for the grid-connected system with a grid-type direct-drive wind turbine:

[0070] 1) Ignore the transient processes of the mechanical rotor and PWM in the grid-type direct-drive fan;

[0071] 2) Assume the DC voltage is stable and ignore the dynamic characteristics of the rotor-side converter;

[0072] 3) Ignoring the dynamics of the current loop and using unity power factor control, the q-axis reference current is 0;

[0073] 4) The voltage loop control parameters are considered constant, and the dynamics of the voltage control loop are not considered in the transient stability analysis of grid-connected wind turbines;

[0074] Based on the above assumptions, a mathematical model of a grid-connected wind turbine system can be constructed, and the phase-locked loop control structure can be obtained as follows:

[0075] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0076] In the formula: U 1,q Let K be the q-axis component of the voltage at U1. p K is the proportional gain of the phase-locked loop. i ω is the integral coefficient of the phase-locked loop. N θ is the system's rated angular frequency. pll This is the output phase angle of the phase-locked loop.

[0077] The distribution pattern of the q-axis components of the voltage at each node on the branch is as follows:

[0078]

[0079] In the formula: ω pll To generate a reference frame for the rotational speed of the grid-type wind turbine control system, L 12 L 13 L 14 θ1, θ2, θ3, and θ4 are the line inductances from node 1 to nodes 2, 3, and 4, respectively, and θ4 are the voltage phase angles at nodes 2, 3, and 4. The power factor angle is the angle under unity power factor control. θ 12 θ 13 θ 14 Let θ be the impedance angle of lines 1-2, 1-3, and 1-4. Since the line resistance is neglected, we have θ 12 =θ 12 =θ 14 =90°; the line current component on the q-axis is Ignoring current loop dynamics, assume I gδ is a constant, and it is the difference between the phase angle of the phase-locked loop output and the phase angle of the voltage at the infinite point.

[0080] Combining the above equation, the equivalent motion equation of the grid-type fan can be expressed as:

[0081]

[0082] In the formula: U1, U2, U3, and U4 are the voltages at nodes 2, 3, and 4, respectively.

[0083] S102: Construct the energy function based on the equivalent motion equation of the grid-type wind turbine.

[0084] In this embodiment, the energy function is constructed using the equivalent motion equation of the grid-connected wind turbine:

[0085]

[0086] In the formula: V is the total energy of the system, V KE For the system's kinetic energy, V PE For the system's transient state energy, V D For the system damping energy, σ k Let σ be the phase angle difference of line k. k,s Let P be the phase angle difference of line k under the steady state of the system, M be the equivalent inertial time constant, and P be the phase angle difference of line k. k (δ) represents the equivalent electromagnetic power, P k,s U is the equivalent power steady-state value, D is the damping coefficient of the grid-connected wind turbine, and U is the damping coefficient of the grid-connected wind turbine. j,q For U j The q-axis component of the voltage at the location, l 1j Let be the line inductance from node 1 to node j.

[0087] S103: Based on the grid-connected infinite bus system of grid-connected wind turbines, extend to multi-machine systems to obtain the state-space expression of the grid-connected multi-machine system of grid-connected wind turbines.

[0088] In this embodiment, the grid-connected infinite bus system of grid-connected wind turbines is extended to a multi-machine system, resulting in the state-space expression of the grid-connected multi-machine system of grid-connected wind turbines:

[0089]

[0090] In the formula, M is the equivalent inertial time constant matrix, ω g To be related to the angular velocity vector of the grid-type wind turbine, T g U is the identity matrix. j,q (α) / (1-K p l 1j I g ω represents the equivalent electromagnetic power of each branch. N l 1j Ig / (1-K p l 1j I g ) represents the steady-state value of the equivalent power of each branch, and D is the damping coefficient matrix of the grid-type wind turbine.

[0091] S104: Based on the state-space expression of the grid-connected multi-machine system and the energy function, construct the branch energy function of the grid-connected multi-machine system. The branch energy function includes the energy function of the whole system and the transient energy function of the multi-machine system.

[0092] In this embodiment, it is assumed that there exists an equilibrium point (α). s Given that the equilibrium point is 0, the energy function for the entire system is established as follows:

[0093]

[0094] In the formula: Let W(α,α) be the kinetic energy function. s Let ) be the potential energy function, where Let V(α,ω) be the damping energy function. g () represents the total energy of the system. M is the transpose of the generator angular velocity vector. g Let ω be the equivalent inertial time constant matrix. g Let α be the generator angular velocity vector. s Let f(α) be the steady-state phase angle of the node voltage relative to the reference point, α be the phase angle of the node voltage relative to the reference point, D be the generator damping coefficient matrix, and f(α) be the generator damping coefficient matrix. s ) represents the steady-state value of the equivalent active power of each branch, and f(α) represents the equivalent active power of each branch;

[0095] Using the branch phase angle difference at the fault clearing moment as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0096]

[0097] Where: V is the total system energy, i is the generator serial number, m is the total number of GFL-PMSG units, and M is the total number of units. i Let ω be the equivalent inertial time constant of the i-th generator. i Let D be the angular frequency of the i-th generator. i Let be the damping coefficient of the i-th generator.

[0098] Considering the impact of synchronous machine grid connection, a multi-machine system can be represented as:

[0099]

[0100] In the formula: Let be the synchronous kinetic energy function of the system. Let be the kinetic energy function of the synchronizer in the system.

[0101] S200: Determine the branch stability discrimination index (BSC) for grid-connected wind turbine systems based on the branch energy function. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If ≠0, the system is transiently stable.

[0102] like Figure 4 As shown, when the system is in a stable state, the transient potential energy of each branch fluctuates within a certain bounded range. The transient potential energy of branch 2-3 shows a significantly higher fluctuation range than that of branches 1-2 and 3-4. Once the system becomes unstable, the transient potential energy of branch 2-3 continuously decreases and is no longer confined to the bounded range, while the transient potential energies of branches 1-2 and 3-4 remain within their bounded ranges. This indicates that the subsystem formed by branches 1-2 and 3-4 is internally stable, but the instability of branch 2-3, which connects these two subsystems, causes a loss of synchronization between the two subsystems, leading to the instability of the entire system.

[0103] In other words, the potential energy of branches in the network distribution exhibits certain regularities. When the system is stable, the potential energy of all branches varies within a bounded range, and the potential energy share of the critical cut set is higher than that of other branches. As the system stability gradually deteriorates, the trend of system potential energy concentrating towards the critical cut set becomes increasingly obvious. In the case of system instability, the potential energy of the critical cut set may even decrease monotonically.

[0104] When the system is unstable, the difference between the equivalent electromagnetic power and the steady-state equivalent power is 0; when the system is stable, the difference between the equivalent electromagnetic power and the steady-state equivalent power is not 0. Based on these characteristics, the branch stability discrimination index (BSC) for grid-connected wind turbine systems is obtained. GFLWT (Grid-Following Wind Turbine Branch Stability Criterion, BSC GFLWT ), defined as:

[0105]

[0106] In the formula: V' PEK (t a ,t b ) = V PEK (t a ,t b ) / (1-K p l 1j I gTo eliminate the form of internal parameters of the grid-type fan, P k (t b ) is branch k in t b The equivalent power P at time t is k,s V represents the equivalent power at the steady moment of branch k. PEK (t a ,t b ) is branch k in (t) a ,t b The change in branch potential energy U within time ) j,q (t b ) for t b The voltage component of node j at time q, U j,q (t0) represents the voltage component of node j at time t0 along the q-axis.

[0107] BSC GFLWT It can determine the changing trend of the branch angle difference. Assuming the initial power flow direction of branch k is positive, in (t a ,t b It exists throughout the time period. That is, [P] k (t)-P k,s ]Δω k (t)>0. Then when Δω k When (t) < 0, there exists [P k (t)-P k,s ] < 0, BSC GFLWT <0; when Δω k When (t)>0, there exists [P k (t)-P k,s >0, BSC GFLWT >0; where, The derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy in branch k, P k (t) represents the equivalent power of branch k at time t, P k,s This represents the equivalent power at the steady moment of branch k.

[0108] The following embodiments of this application will verify the effectiveness of the proposed system stability index using a four-unit, two-zone system including a grid-connected wind turbine.

[0109] like Figure 5 As shown, the effectiveness of the proposed indicators is verified in a 4-machine 2-zone system under GFLWT access.

[0110] This application embodiment proposes BSC GFLWTIt can not only quantitatively analyze the stability of the system, but also assess the impact of each branch and cut set in the network on the transient stability of the system, and identify weak links in the network. The verification process includes the following steps one through three.

[0111] Step 1: Based on branch parameters and branch variables, and combining the characteristics of the phase-locked loop structure and the branch voltage distribution characteristics, construct the energy function of the grid-connected wind turbine system.

[0112] Step 2: Calculate the BSC of each branch of the wide-area measurement information calculation system. GFLWT By comparing the SGPBI values ​​of each branch, the weak points of the system can be identified.

[0113] Step 3: If a branch BSC exists after a fault occurs. GFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If ≠0, the system is transiently stable.

[0114] Figure 6 In the system, when it is in a stable state, the transient potential energy of each branch fluctuates within a certain bounded range. Among these, the transient potential energy of branches 8-9a(b) and 7-8a(b) changes more significantly than the other branches. Once the system becomes unstable, the transient potential energy of branches 8-9a(b) and 7-8a(b) continuously decreases and is no longer confined to the bounded range, while the transient potential energy of other branches remains within the bounded range. This indicates that the cut set formed by branches 8-9a(b) and 7-8a(b) is the weak link in the system. The instability of this cut set causes a loss of synchronization between the two subsystems, leading to the instability of the entire system.

[0115] Table 1. Branch BSC under Stable Conditions GFLWT Calculated value

[0116]

[0117] As can be seen from Table 1, when the system is stable, the BSC of branches 8-9a(b) and 7-8a(b) GFLWT The calculated value is less than that of the other branches, and the corresponding stability is also worse. The cut set formed by it is the weak link of the system.

[0118] Table 2 Branch BSC under Instability GFLWT Calculated value

[0119]

[0120] As can be seen from Table 2, when the system becomes unstable, branches 8-9a(b) and 7-8a(b) are the weakest links in the system, and their BSC... GFLWT The calculated value is 0. The index proposed in this application can be used to determine the stability of the system.

[0121] This application also provides a branch energy transient stability assessment device for a grid-connected wind turbine system, such as... Figure 7 As shown, the branch energy transient stability assessment device for the grid-connected wind turbine system includes:

[0122] Function construction module 701 is configured to construct the branch energy function of the grid-connected wind turbine system based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network.

[0123] The indicator evaluation module 702 is configured to determine the branch stability discrimination index (BSC) of the grid-connected wind turbine system based on the branch energy function. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system will experience transient instability, and the branch BSC will be affected. GFLWT If ≠0, the system is transiently stable.

[0124] In some embodiments, the function building module is further configured to:

[0125] Based on the established assumptions, the equivalent motion equations of the grid-type wind turbine are established;

[0126] Based on the equivalent motion equation of the grid-type wind turbine, an energy function is constructed.

[0127] Based on the grid-connected infinite bus system of grid-connected wind turbines, the state-space expression of the grid-connected multi-machine system of grid-connected wind turbines is obtained by extending to multi-machine systems.

[0128] Based on the state-space expression of the grid-connected multi-machine system and the energy function, the branch energy function of the grid-connected multi-machine system is constructed. The branch energy function includes the energy function of the entire system and the transient energy function of the multi-machine system.

[0129] In some embodiments, the set assumptions include:

[0130] Ignore the transient processes of the mechanical rotor and PWM in the grid-type direct-drive fan;

[0131] Assuming the DC voltage is stable, the dynamic characteristics of the rotor-side converter are ignored;

[0132] Ignoring current loop dynamics and using unity power factor control, there exists a q-axis reference current of 0;

[0133] Assuming the voltage loop control parameters are constant, the dynamics of the voltage control loop are not considered in the transient stability analysis of grid-connected wind turbines.

[0134] The function construction module is further configured as follows:

[0135] A mathematical model of a grid-connected wind turbine system is constructed based on the established assumptions; wherein, the phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows:

[0136] θ pll =∫(K i ∫U 1,q dt+K p U 1,q )dt+∫ω N dt

[0137] In the formula: U 1,q Let K be the q-axis component of the voltage at U1. p K is the proportional gain of the phase-locked loop. i ω is the integral coefficient of the phase-locked loop. N θ is the system's rated angular frequency. pll The phase angle is the output phase angle of the phase-locked loop, and t is time.

[0138] Based on the distribution law of the q-axis component of the voltage at each node on the branch and the phase-locked loop control structure, the equivalent motion equation of the grid-type wind turbine is established.

[0139] The distribution pattern of the q-axis components of the voltage at each node on the branch is as follows:

[0140]

[0141] In the formula: ω pll To generate a reference frame for the rotational speed of the grid-type wind turbine control system, L 12 L 13 L 14 θ1, θ2, θ3, and θ4 are the line inductances from node 1 to nodes 2, 3, and 4, respectively, and θ4 are the voltage phase angles at nodes 2, 3, and 4. The power factor angle is the angle under unity power factor control. θ 12 θ 13 θ 14 Let θ be the impedance angle of lines 1-2, 1-3, and 1-4. 12 =θ 12 =θ 14 =90°; the line current component on the q-axis is I g The value is constant, and δ is the difference between the phase angle of the phase-locked loop output and the phase angle of the voltage at the infinite point.

[0142] The equivalent motion equation of the grid-connected wind turbine is expressed as:

[0143]

[0144] In the formula: U1, U2, U3, and U4 are the voltages at nodes 2, 3, and 4, respectively.

[0145] In some embodiments, the function construction module is further configured to extend from a grid-connected infinite bus system to a multi-machine system, resulting in the state-space expression of the grid-connected multi-machine system of the wind turbine:

[0146]

[0147] In the formula: V is the total energy of the system, V KE For the system's kinetic energy, V PE For the system's transient state energy, V D For the system damping energy, σ k Let σ be the phase angle difference of line k. k,s Let P be the phase angle difference of line k under the steady state of the system, M be the equivalent inertial time constant, and P be the phase angle difference of line k. k (δ) represents the equivalent electromagnetic power, P k,s U is the equivalent power steady-state value, D is the damping coefficient of the grid-connected wind turbine, and U is the damping coefficient of the grid-connected wind turbine. j,q For U j The q-axis component of the voltage at the location, l 1j Let U be the line inductance from node 1 to node j. j Let be the voltage at node j, u be the branch phase angle difference, k be the line number, and t0 be the moment when the system is in steady state.

[0148] In some embodiments, the function building module is further configured to:

[0149] Based on the state-space expression of the grid-connected multi-unit wind turbine system and the energy function, according to the equilibrium point (α) s ,0), establish the energy function for the entire system:

[0150]

[0151] In the formula: Let W(α,α) be the kinetic energy function. s Let ) be the potential energy function, where Let V(α,ω) be the damping energy function. g () represents the total energy of the system. M is the transpose of the generator angular velocity vector. g Let ω be the equivalent inertial time constant matrix. g Let α be the generator angular velocity vector. s Let f(α) be the steady-state phase angle of the node voltage relative to the reference point, α be the phase angle of the node voltage relative to the reference point, D be the generator damping coefficient matrix, and f(α) be the generator damping coefficient matrix. s f(β) represents the steady-state value of the equivalent active power of each branch, and f(β) represents the equivalent active power of each branch.

[0152] Using the branch phase angle difference at the fault clearing moment as the reference point, the transient energy function of the multi-machine system is constructed as follows:

[0153]

[0154] Where: V is the total system energy, i is the generator serial number, m is the total number of GFL-PMSG units, and M is the total number of units. i Let ω be the equivalent inertial time constant of the i-th generator. i Let D be the angular frequency of the i-th generator. i Let be the damping coefficient of the i-th generator.

[0155] In some embodiments, the index evaluation module is further configured to determine the branch stability discrimination index (BSC) of the grid-connected wind turbine system using the following formula. GFLWT :

[0156]

[0157] In the formula: V' PEK (t a ,t b ) = V PEK (t a ,t b ) / (1-K p l 1j I g To eliminate the form of internal parameters of the grid-type fan, K p l is the proportional gain of the phase-locked loop. 1j V is the line inductance from node 1 to node j. PEK (t a ,t b ) is branch k in (t) a ,t b The change in branch potential energy at time ) U j,q (t b ) for t b The voltage component of node j at time q, U j,q (t0) represents the voltage component of node j at time t0 along the q-axis.

[0158] In some embodiments, the branch stability discrimination index is used to determine the changing trend of the branch angle difference, taking the initial power flow direction of branch k as the positive direction, in (t a ,t b It exists throughout the time period. When Δω k When (t) < 0, if BSC GFLWT <0, then [P k (t)-P k,s ] < 0,; ​​when Δω kWhen (t)>0, if BSC GFLWT >0, then [P k (t)-P k,s >0; where, The derivative of the potential energy of branch k, Δω k (t) represents the angular frequency difference of the potential energy in branch k, P k (t) represents the equivalent power of branch k at time t, P k,s This represents the equivalent power at the steady moment of branch k.

[0159] This application provides an electronic device. The electronic device may include a processor and a memory, wherein the processor and the memory can communicate; exemplarily, the processor and the memory communicate via a communication bus.

[0160] The processor executes computer execution instructions stored in memory, causing the processor to perform the scheme in the above embodiments. The processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0161] The communication bus can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The system bus can be divided into address bus, data bus, control bus, etc. Transceivers are used to enable communication between database access devices and other computers (e.g., clients, read-write libraries, and read-only libraries). Memory may include random access memory (RAM) and may also include non-volatile memory.

[0162] The electronic device provided in this application embodiment can be the terminal device described in the above embodiments.

[0163] This application also provides a computer-readable storage medium storing computer instructions. When the computer instructions are executed on a computer, the computer performs the technical solution of the branch energy transient stability assessment method of the grid-connected wind turbine system described above.

[0164] This application also provides a computer program product, which includes a computer program stored in a computer-readable storage medium. At least one processor can read the computer program from the computer-readable storage medium. When the at least one processor executes the computer program, it can implement the technical solution of the branch energy transient stability assessment method of the grid-connected wind turbine system described in the above embodiments.

[0165] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be indirect coupling or communication connection through some interfaces, devices, or modules, and may be electrical, mechanical, or other forms.

[0166] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to implement the solution of this embodiment according to actual needs.

[0167] Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing unit, or each module can exist physically separately, or two or more modules can be integrated into one unit. The unit composed of the above modules can be implemented in hardware or in the form of hardware plus software functional units.

[0168] The integrated modules described above, implemented as software functional modules, can be stored in a computer-readable storage medium. These software functional modules, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute some steps of the methods of the various embodiments of this application.

[0169] It should be understood that the aforementioned processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. A general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly manifested as being executed by a hardware processor, or executed by a combination of hardware and software modules within the processor.

[0170] The memory may include high-speed RAM, and may also include non-volatile storage (NVM), such as at least one disk storage device, and may also be a USB flash drive, external hard drive, read-only memory, disk or optical disc, etc.

[0171] Buses can be Industry Standard Architecture (ISA) buses, Peripheral Component Interconnect (PCI) buses, or Extended Industry Standard Architecture (EISA) buses, etc. Buses can be categorized into address buses, data buses, control buses, etc.

[0172] The aforementioned storage medium can be implemented from any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The storage medium can be any available medium accessible to general-purpose or special-purpose computers.

[0173] An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. Alternatively, the storage medium can be an integral part of the processor. The processor and storage medium can reside in an Application Specific Integrated Circuit (ASIC). Alternatively, the processor and storage medium can exist as discrete components in an electronic control unit or main control device.

[0174] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for evaluating the transient stability of branch energy in a grid-connected wind turbine system, characterized in that, The method includes: Based on the mathematical characteristics of phase-locked loops and the voltage distribution characteristics in the network, the branch energy function of the grid-connected wind turbine system is constructed. Based on the branch energy function, determine the branch stability discrimination index (BSC) for the grid-connected wind turbine system. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system transiently becomes unstable, and the branch BSC... GFLWT If ≠0, the system is transiently stable; Based on the mathematical characteristics of phase-locked loops and the voltage distribution characteristics in the network, the branch energy function of a grid-connected wind turbine system is constructed, including: Based on the established assumptions, the equivalent motion equations of the grid-type wind turbine are established; Based on the equivalent motion equation of the grid-type wind turbine, an energy function is constructed. Based on the grid-connected infinite bus system of grid-connected wind turbines, the state-space expression of the grid-connected multi-machine system of grid-connected wind turbines is obtained by extending to multi-machine systems. Based on the state-space expression of the grid-connected multi-machine system of the grid-connected wind turbine and the energy function, the branch energy function of the grid-connected wind turbine system is constructed. The branch energy function includes the energy function of the whole system and the transient energy function of the multi-machine system. The assumptions set include: Ignore the transient processes of the mechanical rotor and PWM in the grid-type direct-drive fan; Assuming the DC voltage is stable, the dynamic characteristics of the rotor-side converter are ignored; Ignoring current loop dynamics and using unity power factor control, there exists a q-axis reference current of 0; Assuming the voltage loop control parameters are constant, the dynamics of the voltage control loop are not considered in the transient stability analysis of grid-connected wind turbines. Based on the established assumptions, the equivalent motion equations for the grid-type wind turbine are established, including: A mathematical model of a grid-connected wind turbine system is constructed based on the established assumptions; wherein, the phase-locked loop control structure of the mathematical model of the grid-connected wind turbine system is expressed as follows: In the formula: for Voltage at the point q Axial components, This is the proportional gain of the phase-locked loop. The integral coefficients of the phase-locked loop are... The system's rated angular frequency, The phase angle is the output phase angle of the phase-locked loop, and t is time. Based on the voltage of each node on the branch q Based on the distribution law of the shaft components and the phase-locked loop control structure, the equivalent motion equation of the grid-type fan is established. Among them, the voltage of each node on the branch. q The distribution law of the axial components is as follows: In the formula: To generate a reference frame for the rotational speed of the grid-type wind turbine control system, , , These are the line inductances from node 1 to nodes 2, 3, and 4, respectively. , , The voltage phase angles at nodes 2, 3, and 4 are... The power factor angle is the angle under unity power factor control. ; , , The impedance angles for lines 1-2, 1-3, and 1-4 are given. The line current is q Axis components are , For a constant value, To obtain the difference between the phase angle of the phase-locked loop output and the phase angle of the voltage at the infinite point; The equivalent motion equation of the grid-connected wind turbine is expressed as: In the formula: U 1. U 2. U 3. U 4 represents the voltages at nodes 2, 3, and 4, respectively; The effectiveness of the proposed indicators was verified using a 4-unit, 2-zone system connected to GFLWT. This system includes two synchronous generators G2 and G3, two grid-connected wind turbine generators GFLWT1 and GFLWT2, 11 nodes, 4 transformer branches, and 8 AC lines. The 4 transformer branches are branches 1-5, 2-6, 3-11, and 4-10. The 8 AC lines are lines 5-6, 6-7, 7-8 (double circuit), 8-9 (double circuit), 9-10, and 11-10. The area Are is composed of the grid-connected wind turbine generator GFLWT1, the synchronous generator G2, nodes 1, 2, 5, 6, and 7, and their corresponding lines. Area 2 is composed of grid-connected wind turbine generator GFLWT2, synchronous generator G3, nodes 3, 4, 9, 10, 11, and corresponding lines. Node 8 is the hub connecting the two areas. Grid-connected wind turbine generator GFLWT1 transmits power to the grid-connected loads at nodes 6 and 10 via transformer branches 1-5. Synchronous generator G2 transmits power to the grid-connected loads at nodes 6 and 10 via transformer branches 2-6. Grid-connected wind turbine generator GFLWT2 transmits power to the grid-connected loads at node 10 via transformer branches 4-10. Synchronous generator G3 transmits power to the grid-connected loads at node 10 via transformer branches 3-11. The verification process includes the following steps one through three: Step 1: Based on branch parameters and branch variables, and combining the characteristics of the phase-locked loop structure and the branch voltage distribution characteristics, construct the energy function of the grid-connected wind turbine system; Step 2: Calculate the BSC of each branch of the wide-area measurement information calculation system. GFLWT By comparing the SGPBI values ​​of each branch, the weak points of the system can be identified; Step 3: If a branch BSC exists after a fault occurs. GFLWT If the value is 0, the system transiently becomes unstable, and the branch BSC... GFLWT If ≠0, the system is transiently stable.

2. The method for evaluating the transient stability of branch energy in a grid-connected wind turbine system according to claim 1, characterized in that, Based on the grid-connected infinite bus system of grid-connected wind turbines, the system is extended to multiple units, resulting in the state-space expression of the grid-connected infinite bus system of grid-connected wind turbines as follows: In the formula: The total energy of the system. As the system's kinetic energy, For the system's transient state energy, For the system damping energy, For the line k The phase angle difference, For the line in the stable state of the system k The phase angle difference, M The equivalent inertial time constant, For equivalent electromagnetic power, This is the steady-state value of the equivalent power. D To match the damping coefficient of the grid-type wind turbine, for Voltage at the point q Axial components, From node 1 to node j The line inductance, For nodes j The voltage of u For the branch phase angle difference, k For line number, t 0 represents the moment when the system is in a steady state.

3. The method for evaluating the transient stability of branch energy in a grid-connected wind turbine system according to claim 2, characterized in that, Based on the state-space expression of the grid-connected multi-unit wind turbine system and the energy function, the branch energy function of the grid-connected wind turbine system is constructed, including: Based on the state-space expression of the grid-connected multi-unit wind turbine system and the energy function, according to the equilibrium point Establish the energy function for the entire system: In the formula: Let be the kinetic energy function. Let be the potential energy function, where , Let be the damping energy function. The total energy of the system. This is the transpose of the generator angular velocity vector. The equivalent inertial time constant matrix, The generator's angular velocity vector. This represents the steady-state phase angle of the node voltage relative to the reference point. The phase angle of the node voltage relative to the reference point. D Here is the generator damping coefficient matrix. f ( () represents the steady-state value of the equivalent active power of each branch. f ( ) represents the equivalent active power of each branch; Using the branch phase angle difference at the fault clearing moment as the reference point, the transient energy function of the multi-machine system is constructed as follows: In the formula: V The total energy of the system. i Generator serial number m This represents the total number of GFL-PMSG units. M i For the first i The equivalent inertial time constant of a generator. For the first i The angular frequency of the generator. D i For the first i Damping coefficient of a generator.

4. The method for evaluating the transient stability of branch energy in a grid-connected wind turbine system according to claim 1, characterized in that, The branch stability discrimination index (BSC) for grid-connected wind turbine systems is determined using the following formula. GFLWT : In the formula: To eliminate the form of internal parameters of the grid-type fan, This is the proportional gain of the phase-locked loop. From node 1 to node j The line inductance, For branch k in The change in branch potential energy within a given time interval. for Time corresponding node j The voltage at q Axial components, for Time corresponding node j The voltage at q Axial components.

5. The method for evaluating the transient stability of branch energy in a grid-connected wind turbine system according to claim 1, characterized in that, The branch stability discrimination index is used to determine the changing trend of the branch angle difference, with the initial power flow direction of branch k as the positive direction. It exists continuously within a certain time period. ,when At that time, if ,but ,;when At that time, if ,but ,;in, Indicates a branch k The derivative of potential energy, Indicates a branch k The angular frequency difference of potential energy For branch k in t The equivalent power at time t, This represents the equivalent power at the steady moment of branch k.

6. A branch energy transient stability assessment device for a grid-connected wind turbine system, used to implement the method as described in any one of claims 1-5, characterized in that, The device includes: The function construction module is configured to construct the branch energy function of the grid-connected wind turbine system based on the mathematical characteristics of the phase-locked loop and the voltage distribution characteristics in the network. The indicator evaluation module is configured to determine the branch stability discrimination index (BSC) of the grid-connected wind turbine system based on the branch energy function. GFLWT If a branch BSC exists after a fault occurs GFLWT If the value is 0, the system transiently becomes unstable, and the branch BSC... GFLWT If ≠0, the system is transiently stable.

7. An electronic device, characterized in that, include: A processor, and a memory communicatively connected to the processor; The memory stores computer-executed instructions; The processor executes the computer execution instructions stored in the memory to implement the branch energy transient stability assessment method for a grid-connected wind turbine system as described in any one of claims 1-5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the branch energy transient stability assessment method for a grid-connected wind turbine system as described in any one of claims 1-5.

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